Fuel metering apparatus for a carburetor

ABSTRACT

An improved fuel metering apparatus for a carburetor which provides an optimum air/fuel ratio at all engine speeds and loads. The air/fuel ratio is adjusted by means of a valve sensitive to intake manifold pressure which modulates the amount of bleed air mixed with the fuel prior to the aerated fuel being introduced into the venturi throat of the carburetor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to carburetors of the type usedwith internal combustion engines. More particularly, the invention isdirected to an apparatus for matching the air/fuel ratio delivered by acarburetor to the requirements of an engine operating at various speedsand loads.

2. Description of the Prior Art

Precise air/fuel ratio control, especially on engines operating verylean at part load, is absolutely necessary for good driveability andoptimum emissions. When a carburetor is used to mix and meter the airand fuel, it is designed to match as closely as possible the particularrequirements of the engine. In addition to a primary fuel meteringsystem which generally comprises an air induction pipe, a venturithroat, a fuel nozzle and a throttle plate, it is not uncommon to employother systems to tailor the output of the carburetor to the requirementsof the engine. For example, choke systems are often incorporated toimprove cold starting and running characteristics of the engine, idlesystems are used to facilitate low speed engine operation andaccelerator pump systems are sometimes used to prevent stalling byinjecting an additional quantity of fuel when the throttle plate israpidly opened.

The primary fuel metering system .[.is.]. .Iadd.in .Iaddend.a carburetoris usually adjusted to deliver an air/fuel ratio which is appropriatefor mid-range engine load conditions. Thus, as engine load increases,the air/fuel ratio provided by the primary fuel metering system must beenriched to obtain the most efficient operating conditions. Thisrequired engine enrichment is frequently accomplished with a power jetsystem which at a predetermined point augments the quantity of fuelbeing delivered at the venturi throat.

A power jet mixture enrichment system can only approximate an engine'srequirements. It cannot proportionately respond to increasing engineloads as it is either on or off and is usually adjusted to meet theengine's requirements under maximum load conditions. Generally, atengine loads greater than normal but less than those required to kick inthe power jet, the engine is running lean. At loads sufficiently high toactuate the power jet, but less than full power, the engine runs toorich. Because of these inaccuracies associated with metering the fuel,optimum performance is not obtained over the full range of engineoperating conditions. This results in higher fuel consumption and higherexhaust emission levels.

In internal combustion engines equipped with carburetors andturbochargers it is desirable to locate the carburetor between the aircompressor discharge and the intake manifold as such placement resultsin superior mixing of the fuel with the air. However, given the presentstate of the art, it is extremely difficult to so position thecarburetor when high load enrichment is obtained with a power jet systemhaving a bleed air feature because at high loads, the compressor "boost"applied through the air bleed creates a high air flow which leans outthe mixture at a time when it should be enriched.

SUMMARY OF THE INVENTION

One of the principal objects of the present invention is to provide animproved fuel metering apparatus for a carburetor which is able todeliver the optimum air/fuel ratio to an internal combustion engine overa wide range of speeds and loads. By providing the optimum air/fuelratio throughout the operating range of an engine, the inventionimproves performance and reduces fuel consumption while lowering theemission of toxic exhaust pollutants such as carbon monoxide. Theinvention also provides a fuel metering system that can be used withturbocharged engines and is easily incorporated in a carburetor disposedbetween the compressor discharge and the intake manifold of the engine.

The present invention accomplishes these diverse objects by monitoringthe intake manifold pressure or throttle position (both being functionsof engine load and hence mixture requirement) and continuouslymodulating the quantity of air being bled into the fuel by means of avalve responsive to the manifold pressure or throttle position. Thequantity of fuel delivered to the venturi of the carburetor variesinversely with the bleed air and thus this is an effective way tocontrol the air/fuel mixture delivered to the engine.

The many objects and advantages of the present invention will be bestunderstood by those skilled in the art when the following description ofthe best mode contemplated for practicing the invention is read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying drawings in which like orsimilar elements appearing throughout the several views are referred toby the same reference characters and in which:

FIG. 1 is a diagrammatic view in partial cross section showing theinvention in relationship to other carburetor components;

FIG. 2 is a diagrammatic view in partial cross section of a conventionalpower jet system and a conventional bleed air system for a carburetor;

FIG. 3 is a .[.cross sectional.]. .Iadd.cross-sectional .Iaddend.view ofan intake manifold pressure sensing and bleed air modulating valve ofthe present invention;

FIG. 4 is a .[.cross sectional.]. .Iadd.cross-sectional .Iaddend.view ofan alternative embodiment of the valve shown in FIG. 3; and

FIG. 5 is a graph depicting the air/fuel curve for an engine which thedevice of the present invention is capable of tracking.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is now made to FIG. 1 which is a diagram in partial crosssection of a carburetion system incorporating the present invention. Thesystem includes an air induction pipe 10 and an air filter (not shown)which is normally positioned on the upper end of air induction pipe. Airis caused to flow through the air induction pipe 10 in the direction ofthe arrows and passes an annular fuel nozzle 12 (or other conventionalfuel discharge means) which is located in a venturi throat 14 of thepipe 10. The flow of air through the venturi throat 14 causes fuel 16 tobe drawn through apertures 18 in the fuel nozzle 12. These apertures 18in the fuel nozzle 12 are in fluid communication with a pipe 22 which inturn communicates with a main fuel metering jet 24 through anemulsifying well 26. The main fuel metering jet 24 is located along apipe 30 which interconnects the emulsifying well 26 with a fuel bowl 28.A typical butterfly type throttle valve 20 used to control the air flowis shown disposed in the air induction pipe 10 downstream of the venturithroat 14.

Disposed in the emulsifying well 26 is an emulsifying tube 34 having alongitudinal bore 36 and a plurality of passageways 38 which allow fluidcommunication between the exterior surface of the emulsifying tube 34and the longitudinal bore 36.

What has been described to now is conventional with present carburetorsalthough of course different versions exist. The present invention isdirected to such a system including a bleed air modulator valve shownschematically at 44 in FIG. 1. The bleed air modulator valve 44 isprovided with three fluid connections. These fluid connections arerepresented in FIG. 1 by lines 46, 48 and 50. The line 46 is a fluidconnection which supplies filtered air to the bleed air modulator valve44 preferably from the air induction pipe 10 at a point downstream ofthe air filter (not shown) and upstream of the venturi 14. The line 48represents the bleed air output from the modulator valve 44 and is influid communication with a bleed air inlet 32 on the emulsifying well 26through a well vent restrictor 54. The line 50 represents a fluidconnection between the interior of the intake manifold of the engine(not shown) and the modulator valve 44. It is apparent that if desiredthe valve 44 can be mechanically activated by positive linkage to theshaft of the throttle valve 20.

FIG. 2 shows diagrammatically those elements of a carburetor which areconventionally used to provide a power jet system and a bleed airsystem. The power jet system comprises a normally closed, auxilliaryfuel metering jet 52 in parallel with the main fuel metering jet 24.During normal operation fuel 16 from the fuel bowl 28 flows through themain fuel metering jet 24 in the pipe 30 to the emulsifying well 26. Therate of fuel flow through the pipe 30 is controlled by the diameter ofthe main fuel metering jet 24. The rate of fuel flowing into theemulsifying well 26 is increased when the fuel is also allowed to flowthrough the power jet 52. The jet 52 is opened in response to engineload as represented by manifold vacuum or throttle position.

In the conventional construction of a bleed air system shown in FIG. 2filtered air from the air induction pipe 10 communicates with the inlet32 on the emulsifying well 26 through a fixed orifice 54 which is usedto control the flow of air. The bleed air entering the emulsifying well26 through the inlet 32 moves down along the inside of the emulsifyingtube 34, passes through the apertures 38 into the emulsifying well 26while mixing with the fuel 16. This air/fuel mixture is then drawn outof the emulsifying well 26 by the vacuum at the venturi throat 14 andflows through the pipe 22 to the annular fuel nozzle 12. A bleed airsystem of the type herein described is used to preliminarily mix the airand the fuel prior to this mixture being introduced into the venturithroat 14 of the air induction pipe 10 and secondarily to affect somedegree of air/fuel ratio control by uncovering more air holes 38 as thefuel level drops with increasing load and/or speed, thus further leaningout the mixture.

FIG. 3 shows a first embodiment of a manifold pressure sensitive bleedair modulator valve of the type identified schematically in the brokencircle 44 of FIG. 1 and it replaces both the bleed air system and thepower jet system shown in FIG. 2. The valve 44 comprises a cyclindricalhousing 56 in which is disposed a diaphragm 58 which divides theinterior of the housing into a vacuum chamber 60 and an air chamber 62.The vacuum chamber 60 is provided with an inlet pipe 64 whichcorresponds to the line 50 of FIG. 1 and is therefore connected with theintake manifold of the engine. A compressible coil spring 66 or otherbiasing means is interposed between the diaphragm 58 and the housing 56and is biased to expand the volume of the vacuum chamber 60 by forcingthe diaphragm 58 to the left. An air inlet pipe 74 is integrallyattached to the vacuum diaphragm housing 56. The pipe 74 corresponds toline 46 of FIG. 1 and is therefore connected to the induction pipe 10upstream of the venturi 14. The longitudinal axis of the exhaust pipe 68is perpendicular to and passes through the center of the diaphragm 58. Amovable tubular regulating valve 70 is telescopically disposed andslidably movable within the end of the exhaust pipe 68. The valve 70 andthe exhaust pipe 68 are close fitting. One end of the regulating valve70 is integral with the diaphragm 58. A plurality of critically spacedand dimensioned apertures 72 is provided above the length of the valve70. These apertures 72 are sequentially covered and uncovered as thediaphragm 58 moves back and forth causing the valve 70 to slide in andout of the exhaust pipe 68. The end of the tubular valve 70 opposite thediaphragm 58 is open. The outlet pipe 68 corresponds to the line 48 ofFIG. 1 and is thus connected to the inlet 32 of the emulsifying well 26through the well vent 54.

The valve shown in FIG. 3 is for part-time operation, since it onlycontrols the air/fuel ratio over a part of the engine's load range. Thisembodiment in essence replaces the functions of the hereinbeforedescribed power jet system. In so doing, it provides better control ofthe air/fuel ratio, and allows the high load control function to bematched exactly to the requirements of the engine and/or the wishes ofthe engine developer. With limitations it also replaces part of thefunctions of a vacuum operated accelerating pump.

A second embodiment of a manifold pressure sensitive bleed air modulatorvalve of the present invention is shown in FIG. 4. This embodiment isadapted to operate over an extended range of engine speeds and loads. Itdiffers from the valve shown in FIG. 3 in that the end of the movabletubular regulating valve 170 which is not integrally attached to thediaphragm 58 is provided with an end wall 78 and a plurality ofcritically spaced and dimensioned apertures 80 are disposed adjacent thewall 78. Additionally, an auxilliary housing 82 is integrally disposedat the end of a tubular valve housing 168 forming an auxilliary chamber84 in which the regulating valve 170 may reciprocate. The outlet pipe 68is connected with the auxilliary chamber 84. An optional coil biasingspring 76 is shown coaxially disposed within the coil spring 66 toprovide a predetermined composite spring response. Multiple springs canalso be used if desired to tailor the response of the FIG. 3 embodiment.

In FIG. 5, the relative fuel/air ratio is shown increasing from bottomto top along the vertical axis 88. The intake manifold vacuum measuredin inches of mercury is shown decreasing from left to right long thehorizontal axis 90. This decrease in manifold vacuum is associated withless throttle plate restriction and higher engine loads. The curverepresented by solid line 92 represents the optimum air/fuel ratio overa wide range of operating conditions. The apparatus of this invention iscapable of tracking this curve. The optimum air/fuel ratio for enginestarting is shown at point 94. A leaner mixture is required under normaloperating conditions shown at point 96. Point 98 shows that a richmixture is required under maximum load conditions.

The apparatus of this invention and a well designed conventionalcarburetor are both able to track the curve 92 between the optimumstarting conditions at point 94 and the normal operating conditionsshown at point 96. Past the point 96 a conventional carburetor equippedwith a main fuel metering system delivers a mixture which follows thedashed line to the point 100. A shaded area 102 highlights the disparitybetween the engine's requirements and the inadequate mixtures beingsupplied by a conventional carburetor. If the carburetor is not equippedwith a mixture enrichment system then it is impossible to obtain themaximum power from the engine. Conventional carburetors equipped withpower jet systems may or may not track the curve from point 94 to point96 and then deliver a lean mixture up to the point 100 when the powerjet kicks in and immediately provides a mixture indicated by the point104 which is too rich for the engine's requirements. The delivery ofthis overrich mixture takes place at manifold vacuums between 3 to 7 in.Hg. and continues until the engine is operating at maximum power whichis indicated at point 98. The shaded area 106 highlights the excessivelyrich mixture delivered by a conventional power jet system.

Referring now to FIGS. 1 and 3 for a description of the operation of thepresent invention, when starting the engine the regulating valve 70 ispositioned all the way to the left by the spring 66 and the apertures 72are closed as desired by the outlet pipe 68. When the valve is in thisposition, air flow from the induction pipe 10 is either cut off orrestricted, as desired from entering the bleed air inlet 32 on theemulsifying well 26. The air/fuel mixture is now suitable for starting(enriched). As the engine starts the manifold vacuum increases, movingthe diaphragm 58 to the right and drawing the valve 70 with it. Thismovement uncovers the apertures 72 in the valve 70 and air passes fromthe air induction pipe 10 through the inlet 74, through apertures 72into the hollow valve 70, out the pipe 68 (48 in FIG. 1) through therestrictor (well vent) 54, into the emulsifying tube 36 throughapertures 38 mixing with the fuel, through the pipe 22, and finally intothe venturi throat 14 and the nozzle 12. During light duty operation thevalve 70 is positioned all the way to the right by the manifold vacuumactuating the diaphragm 58 against the spring 66. During this range ofoperation, the air/fuel ratio is controlled in the normal fashion, thatis, by the restrictor 54 and the size and location of the apertures 38in the emulsifying tube 34, with the apertures 72 in the valve 70 actingas a fixed air orifice. This leans out the air/fuel mixture from thatexisting at the starting condition, in the appropriate rate for eachparticular part load condition.

As the load increases to the point where it is desirable to startenriching the mixture, manifold vacuum decreases and the spring 66 movesthe diaphragm 58 and the valve 70 to the left. This movement covers someof the apertures 72 which restricts the flow of air through the outletpipe 68 into the emulsifying well 26 which progressively enriches theair/fuel mixture or compensates from the ever increasing tendency tolean out which is inherent in the basic design of systems with fixedrestrictors. As the engine load increases, the valve 70 is moved furtherto the left until at maximum power (point 98 shown on the graph in FIG.5) the apertures 72 are covered in the desired fashion to either cut offair bleed entirely or to allow the desired amount. By proper sizing andpositioning of the apertures 72 in the valve 70, or by using a variablerate spring 66, or a variable area diaphragm 58, it is possible toobtain the desired air/fuel ratio at the high load condition covered bythe actuation of this device.

Referring now to FIGS. 1 and 4, the operation of the present embodimentis similar to the operation of the embodiment hereinbefore describedexcept that a dual set of air flow regulating apertures 72 and 80 areprovided at both ends of the regulating valve 70 which allows moreprecision in the metering of the bleed air. Operation of the modulatorof FIG. 4 is continual so that the device operates as a full-timecontrol over the total load range of the engine.

With the embodiment of FIG. 4 the diaphragm 58 is also positioned all ofthe way to the left by springs 66 and 76 upon starting the engine. Inthis position of the diaphragm 58 the apertures 72 are totally orpartially covered and therefore communication between the bleed inlet 74and the outlet 68 is closed or highly restricted. Since little or no airis delivered to the emulsifying well 26 an enriched mixture is deliveredto the fuel nozzle 12 for starting the engine.

As the engine starts and manifold vacuum increases the diaphragm 58moves to the right to a position dependent upon the increase in manifoldpressure. Air is now delivered from inlet 74 through apertures 72 and 80to the outlet 68. The rate of air flow to outlet 74 is dependent uponthe size, location and number of apertures 80 and 72 which are uncoveredand thus upon manifold pressure.

Further.[.,.]. leaning out of the mixture can be achieved for part loadconditions by disposing the springs 76 so that the valve 170 will startmoving to the left with small decreases in manifold vacuum as wouldresult from light increases in load. In this manner the air/fuel ratiocan be leaned out to a point such as 96 in FIG. 5, nearly correspondingto the largest total area opened by a combination of apertures 72 and80. From this point, if it is desirable to start enriching the mixtureto accommodate higher loads, further throttle opening resulting inmanifold vacuum decreases causes further movement of the diaphragm 58and the valve 170 to the left. In this way the so-called "fuel hook" orair/fuel ratio to engine load curve (FIG. 5) can be tailored exactly tothe requirements of the engine.

As manifold .[.pressures.]. .Iadd.pressure .Iaddend.varies withvariation in load, the diaphragm 58 continually moves back and forth toprovide the optimum fuel/air ratio called for by the engine.

It has been found that the apparatus of the present invention acts as ananti-stall device especially when used in conjunction with venturis ofrelatively small size. If the engine is running at a particular speedand the load increases, the engine speed drops and the manifold vacuumdecreases. In a normal construction, especially if the engine isoperating at very lean air/fuel ratios, the engine would stall becausenot enough fuel can be pulled into the intake manifold. In theconstruction of the present invention, the air manifold diaphragm movesto a closed position and this provides a richer mixture which avoidsstalling.

When an internal combustion engine equipped with a conventionalcarburetor system is coupled with a turbocharger (as illustrated inphantom in FIG. 1 at 108) having its compressor discharge upstream ofthe carburetor, the conventional power jet and bleed air systems do notfunction properly. When the engine is required to deliver high power thepower jet system kicks in and the compressor begins to create a positivemanifold pressure. The fixed bleed air inlet orifice 54 is designed toproperly control the air flow only at normal atmospheric pressures. Thecompressor 108 actually forces excessive quantities of air through thebleed air inlet 32 into the emulsifying well 26 excessively leaning theair/fuel mixture.

The fuel metering system of the present invention allows the properpositioning of the carburetor between the air compressor 108 and theinlet manifold while providing the desired air/fuel ratio withoutdetrimental effects. It will be understood by those familiar with theart that the apparatus must be "matched" to these turbochargedoperations, by proper positioning and sizing of the apertures in theregulating valve 70, and by proper selection of the spring 66 or, ifpreferred by providing a spring 77 as shown in FIG. 4. An additionalspring 76 may be required according to the application, for properair/fuel ratio modulation during the periods when the engine operateswith a positive pressure in the intake manifold. If so desired, theapparatus can also be used as a "power limiter" if the valve 70 isprevented from restricting the flow of all bleed air through theapertures 72, thus allowing a controlled and limited amount of bleed airinto the emulsifying well 26. In this fashion, the maximum amount offuel drawn by the engine can be controlled and the engine power can beeffectively checked.

Although an air valve means has been described which utilizes adiaphragm responsive to manifold pressure it should be apparent thatother means sensing engine load and operating the air valve in responseto changes in such load could be used as well. It should also beunderstood that the system of the present invention could withmodifications be used to regulate air/fuel flow in a fuel injectionsystem rather than the carburetor system shown.

It will also be understood by those familiar with the art, that thedevice of the present invention can also be used with a natural gas orLPG carburetor, either as an air modulator or fuel modulator, or both,to provide the correct air/fuel ratio, as desired.

It should also be understood that an air modulator of the presentinvention could be provided with appropriate means, such as an aneroidor temperature sensing means, to regulate the air/fuel ratio in responseto changes in altitude or temperatures.

Although the system of the present invention has been described with thepipe 68 connected to the emulsifying well 26 and the pipe 74 connectedto the air induction pipe 10 it should be understood that theseconnections can be reversed. With such reversed connections air from theinduction pipe 10 would pass through the apertures 72, the chamber 62and the pipe 74 to the emulsifying well 26.

The system of the present invention is provided with relatively largefuel and air apertures. This reduces the likelihood of clogging andreduces manufacturing costs by diminishing the need to adhere to closetolerances. The relatively rugged design with few operating parts alsoreduces such costs while at the same time reducing maintenancerequirements.

From the foregoing detailed description it will be evident that thereare a number of changes, adaptations, and modifications of the presentinvention which come within the province of those skilled in the art,however, it is intended that all such variations not departing from thespirit of the invention be considered as within the scope thereof aslimited solely by the appended claims.

I claim:
 1. In combination: an internal combustion engine having anintake manifold, an air induction pipe, a venturi throat disposed withinsaid air induction pipe, a fuel reservoir, a fuel nozzle meansconnecting said fuel reservoir and said fuel nozzle means including anemulsifying well disposed intermediate said fuel reservoir and said fuelnozzle means, said fuel nozzle means disposed in said venturi throat forintroducing fuel into a stream of air flowing through said air inductionpipe,said emulsifying well including a passage means for directing airinto the fuel whereby the fuel delivered to said venturi throat is mixedwith air. means in communication with the interior of said intakemanifold for sensing the pressure therein; and valve means connectedintermediate said air induction pipe, upstream of said fuel nozzlemeans, and said emulsifying well, said valve means being connected toand responsive to said manifold pressure sensing means to regulate airflow through an outlet to said emulsifying well to decrease the amountof air introduced into said fuel upon a predetermined increase in thepressure in said intake manifold and to increase the amount of airintroduced into said fuel upon a predetermined decrease in the pressurein said intake manifold whereby a predetermined optimum air/fuel mixtureis provided for said internal combustion engine over a wide range ofengine speeds and loads said valve means comprising a tubular memberhaving apertures therein connecting the interior thereof in the areaadjacent said manifold pressure sensing means to said outlet.
 2. Theimproved fuel metering apparatus described in claim 1 wherein saidmanifold pressure sensing means is a vacuum diaphragm unit.
 3. The fuelmetering apparatus as defined in claim 1 and in which said valve meanscomprises a housing defining a first chamber and a second chamberseparated by a diaphragm, means connecting said second chamber to theintake manifold of an internal combustion engine whereby said diaphragmis actuated in response to changes in the manifold pressure of saidengine, an inlet connecting said first chamber with a source of air andsaid outlet connected with said emulsifying well and said valve membercarried by said diaphragm and operable to variably regulate air flowthrough said outlet in response to movement of said diaphragm.
 4. Thefuel metering apparatus as defined in claim 3 and in which said valvemember extends into said outlet.
 5. The fuel metering apparatus asdefined in claim 4 and in which said valve member further comprises atubular member open at the end toward said outlet.
 6. The fuel meteringapparatus as defined in claim 4 and in which said valve member furthercomprises a tubular member closed at the end toward said outlet.
 7. Thefuel metering apparatus defined in claim 1 and including a turbochargerhaving its compressor discharge upstream of the fuel nozzle. .Iadd.
 8. Afuel metering system for an internal combustion engine, said systemcomprising an air induction pipe, a fuel reservoir, a fuel nozzle meansfluidly connected with said fuel reservoir, a fuel/air mixing meansfluidly connected with said fuel nozzle, said fuel nozzle means disposedin said air induction pipe for introducing a fuel/air mixture fuel intoa stream of air flowing through said air induction pipe,means forsensing engine operation conditions, variable valve means fluidlyconnected with said fuel/air mixing means, to vary the amount of airintroduced into said fuel in said fuel/air mixing means, said valvemeans being operatively connected to and responsive to said means forsensing engine operating conditions, said valve means further comprisinga housing having an interior chamber, an air inlet connected to saidinterior chamber and conduit means for connecting said interior chamberwith said fuel/air mixing means, a portion of said conduit meansadjacent said housing forming a tubular valve seat, a tubular valvemember having a plurality of longitudinally spaced apertures formedtherethrough, said valve member being longitudinally slidably engagedwith said valve seat so that the number of apertures in the valve memberopen to both the interior of the valve seat and the interior chamber isdependent upon the longitudinal position of the valve member withrespect to the valve seat, wherein said sensing means is connected toand controls the longitudinal position of said valve member..Iaddend..Iadd.
 9. A fuel metering system for an internal combustionengine, said system comprising an air induction pipe, a fuel reservoir,a fuel nozzle means fluidly connected with said fuel reservoir, fuel/airmixing means fluidly connected with said fuel nozzle means, said fuelnozzle means disposed in said induction pipe for introducing fuel into astream of air flowing through said air induction pipe, means for sensingambient conditions, and valve means for varying the amount of airintroduced into said fuel upon a change in the ambient conditions assensed by said ambient condition sensing means, said valve means furthercomprising a housing having an interior chamber, an air inlet connectedto said interior chamber and conduit means for connecting said interiorchamber with said fuel/air mixing means, a portion of said conduit meansadjacent said housing forming a tubular valve seat, a tubular valvemember having a plurality of longitudinally spaced apertures formedtherethrough, said valve member being longitudinally slidably engagedwith said valve seat so that the number of apertures in the valve memberopen to both the interior of the valve seat and the interior chamber isdependent upon the longitudinal position of the valve member withrespect to the valve seat, wherein said sensing means is connected toand controls the longitudinal position of said valve member. .Iaddend..Iadd.
 10. A fuel metering system for an internal combustion engine,said system comprising an air induction pipe, a venturi throat disposedwithin said air induction pipe, a fuel reservoir, a fuel/air mixingmeans fluidly connected with said fuel reservoir, fuel nozzle meansfluidly connected with said fuel/air mixing means whereby a fuel/airmixture is delivered to said fuel nozzle means, said fuel nozzle meansdisposed in said venturi throat for introducing said fuel/air mixtureinto a stream of air flowing through said air induction pipe, means forsensing engine operating conditions, valve means connected intermediatesaid air induction pipe and said air mixing means, upstream of said fuelnozzle means, to vary the amount of air introduced into said fuel inaccordance with a variation in the operating conditions of said engine,said valve means further comprising a housing having an interiorchamber, an air inlet connected to said interior chamber and conduitmeans for connecting said interior chamber with said fuel/air mixingmeans, a portion of said conduit means adjacent said housing forming atubular valve seat, a tubular valve member having a plurality oflongitudinally spaced apertures formed therethrough, said valve memberbeing longitudinally slidably engaged with said valve seat so that thenumber of apertures in the valve member open to both the interior of thevalve seat and the interior chamber is dependent upon the longitudinalposition of the valve member with respect to the valve seat, whereinsaid sensing means is connected to and controls the longitudinalposition of said valve member. .Iaddend..Iadd.
 11. A fuel meteringsystem for an internal combustion engine, said engine having an intakemanifold, said system comprising an air induction pipe, fuel/air mixingmeans and means fluidly connecting said fuel/air mixing means with saidair induction pipe, means introducing air into said fuel/air mixingmeans and including valve means operable when actuated to vary the rateof air delivered to said fuel/air mixing means, and means sensingchanges in engine operating conditions and actuating said valve means toregulate the rate of air delivered to said fuel/air mixing means inaccordance with changes in the operating conditions of said engine, saidvalve means further comprising a housing having an interior chamber, anair inlet connected to said interior chamber and conduit means forconnecting said interior chamber with said fuel/air mixing means, aportion of said conduit means adjacent said housing forming a tubularvalve seat, a tubular valve member having a plurality of longitudinallyspaced apertures formed therethrough, said valve member beinglongitudinally slidably engaged with said valve seat so that the numberof apertures in the valve member open to both the interior of the valveseat and the interior chamber is dependent upon the longitudinalposition of the valve member with respect to the valve seat, whereinsaid sensing means is connected to and controls the longitudinalposition of said valve member. .Iaddend. .Iadd.
 12. The system asdefined in claim 11 and in which said engine condition sensing meanscomprises means sensing the manifold pressure of said engine. .Iaddend..Iadd.
 13. The invention as defined in claim 11 wherein said valvemember is slidably received within the interior of the valve seat..Iaddend.